System and method for active vibration isolation and active vibration cancellation

ABSTRACT

The invention relates to a system and method for vibration isolation and cancellation, especially but not exclusively suited for a damper in wafer-chip production equipment. Active vibration isolation and cancellation technology (or air mount technology) for chip production equipment needs to become more effective with the advancement of the production of chips that require ever-smaller features. Typically, actuators and sensors in an active isolation/cancellation system are frequently used but not optimized in their technology. By integrating the actuators and the sensors together certain performance limitations become negligible and can be discarded. The resulting damper can be of an absolute or of a relative damper type. The performance of a vibration isolation and cancellation system and its limitations can be described using gain and phase relations from the control theory. A damper that uses the proposed system is of a so-called absolute damper type.

This application claims the benefit of Provisional application No.60/414,375 filed Sep. 27, 2002.

FIELD OF THE INVENTION

The invention relates to a vibration isolation and cancellation systemand method, especially but not exclusively suited for high precisionwafer-chip production and inspection equipment.

BACKGROUND ART

Products that make use of active vibration isolation and cancellationtechnology are available commercially, but their degree of effectivenessleaves room for improvement. Active vibration isolation and cancellationtechnology (also known as air mount technology) for IC production andinspection equipment needs to become more effective with the advancementof the production of chips that require ever-smaller features.Typically, actuators and sensors in an active isolation/cancellationsystem are not integrated. For instance, U.S. Pat. No. 6,286,644 toWakui discloses and describes an active vibration isolator wherein inFIG. 7 sensors ‘P0’ and air spring actuators ‘AS’ are separate elements.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an active vibrationisolation/cancellation system that integrates an actuator and a sensor.The system provides a much improved vibration cancellation behavior. Thesystem is useful for, amongst others, virtual all types of highprecision production equipment, e.g., in an air-mount for chipproduction equipment, high precision microscopes and other highprecision equipment. The application of the system, for instance,reduces an important barrier in the quest for chips with smallerfeatures. The invention is based on a notion that an actuator and asensor in an active vibration isolation/cancellation system can beintegrated in such a way that many known performance limits (such asdescribed by gain and phase relations from well known control theory)are removed to a degree where they are no longer a performancelimitation.

It is another object of the invention to apply the proposed activevibration isolation/cancellation system in an absolute damper. Bycombining damper technology with air mount technology, a much improvedair mount performance is achieved. The absolute type of (motion) damperof the invention typically but not exclusively comprises two parts thatare displaceable relative to one another, at least in the direction tobe damped. The first part of this type of damper, that may comprise anactuator coil and a complete sensor assembly, is connected to a firstbody (typically a mass to be damped). In case the sensor of this type ofsensor is of a magnet and coil type, one part, e.g. the sensor-coil, isconnected to the first body and the other part, e.g., the sensor-magnetof the invention, may be loosely connected to the first body withrespect to motion that needs to be damped. The inventor proposes toattach the sensor-magnet to a reference mass that is supposedly notnegatively affected by vibrations from other bodies. The reference masscan be realized by a floating mass (loosely connected to the firstbody). This floating mass acts in an absolute damper as an absolutereference. The second part of this type of damper, that may comprise anactuator magnet, is stiffly connected to a second body (typically afloor or reference without motion). The second body is only requiredwith respect to the operation of the damper for providing a reactionforce as reaction of the action force on the first body by the actuator.It is also possible to use an additional body in which to store thereaction forces. This will give at low frequencies a lower level ofperformance, but can be preferable in certain cases. In the descriptionsabove and below, the locations of coils and magnets could be exchangedwithout affecting the general idea of this invention. Whether or not toswap the locations of the coils and magnets is a discussion that dependson many factors and might change from one implementation to another.Typically however, it is preferred to mount the component with thelowest inertia to the body whose motion is to be damped or controlled

Various aspects of the invention are however also applicable for arelative damper and therefore not limited to the absolute damper. Therelative type of (motion) damper typically comprises two parts that aredisplaceable relative to one another, at least in the direction to bedamped. The first part of this type of damper, that may comprise anactuator coil and a sensor coil, is stiffly connected to a first body.The second part of this type of damper, that may comprise an actuatormagnet and a sensor magnet, is stiffly connected to a second body.

In a preferred embodiment a Lorenz type coil as a sensor and another oneas a actuator is used due to their close-to-ideal performance. By usinga specific coil design a potential cross talk between the coils of thesensor and the actuator can be minimized to a level where it can bediscarded. A damper provides an opposing force to velocity. Since Lorenztype of coils (also called voice coils) can sense velocities and canprovide forces, they are appealing candidates as sensors and actuators.In practical implementations (such as in an active air mount) they are,for that and other reasons, frequently used. Other types of sensors andactuators can also be used. They might however require signalconditioning or other operations to make them applicable. An example ofanother type of sensor is a laser interferometer.

An important aspect of the invention lies in the observation that thesensor and the actuator of are preferably mounted in such a way that thecombination (that is part of the damper) possesses certain relevantproperties. One of the relevant properties is that the travel time for amechanical signal caused by the actuator to the sensor is small. Afterthe actuator induces a mechanical movement the sensor measures themechanical movement. The sensor and the actuator combination of theinvention have an acoustic delay, in a preferred embodiment, of far lessthan one millisecond (typically faster than 40 microseconds). Also themass in the direct path between the sensor and actuator should beminimized while the stiffness should be maximized. All theseprescriptions can be achieved by placing the sensor and actuatorsubstantially close to each other. Having a limited travel time for themechanical signal, without any substantial cross talk (between theactuator and the sensor) allows the damper to have a high gain feedbackcontrol loop without having any instability. Moreover the damper of theinvention preferably, although not exclusively, has an electrical delay(that is between the sensor and the actuator) of less than onemicrosecond. That means that on detection by the sensor of a signalcaused by a mechanical movement, a quick reaction is possible (that iscommanding the actuator to generate a force).

It is yet another object of the invention to minimize crosstalk andinterferences, in particular between the actuator and the sensor. Theinventor found that crosstalk is reduced, amongst others, by using amagnetical type of actuator and a non-magnetical type of sensor. Anexample of a non-magnetical type of sensor is an optical one. Anadditional novel manner to achieve a minimum of unwanted cross talk isto place an actuator-coil and a sensor-coil perpendicular relative toeach other. By doing so a magnetical field induced by the actuator-coilof the actuator will cause a minimum of induced current in a sensor-coilThe sensor coil does not generate a field, so the cross talk concernsonly in one way.

By having two instead of one sensor coil, and by using magnets ofopposite polarityin the reference body, two sensors are made that giveopposite signals when a motion is present, but they give an equal signalwhen an electrical or magnetical disturbance is present. By subtractingthe two sensor signals, the measurement of the motion is amplified, andall common disturbances are cancelled. An equally effective method is touse identical magnet arrangements and an opposite coil windingdirection.

The inventor found another way to reduce unwanted cross talk by using ashielding between the actuator and the sensor. When applying a shieldingcomprising an electrical conductor (e.g., copper shielding), a shieldingis achieved for EM waves. The latter type of shielding is alsobeneficial for reducing negative effects caused by external EM sources(e.g. caused by 50/60 Hz mains supply wiring). A shielding should beapplied between the sensor and the actuator and or the external EMsource. For instance, the sensor and or actuator can be packed with acopper foil. In order to reduce unwanted magnetical cross talk amagnetical shielding needs to be applied. This can be achieved by, e.g.,surrounding the sensor coil(s) with so-called μ-metal.

The inventor also found that when covering the damper with a coveragainst noise the performance of the damper is further increased. Thatis because the inventor found that acoustical waves act as currentinducing disturbances on the coil. The inventor found that it isadvantageous to provide an acoustical shield in the absolute type ofdamper, in particular around the floating reference mass. This shieldshould have no contact with the reference mass. In a typical but notexclusive embodiment, the sensor-magnet is to be loosely connected tothe mass to be damped. When the actuator coil is fed by an ideal currentsource, a movement of the second body cannot induce a current in theactuator coil. The second body (to which the actuator magnet is mounted)is only present to provide a reaction force of an action force of theactuator (otherwise no movement could be induced to the mass to bedamped). When the current source is designed to be close to idealsource, little to no disturbance is expected from a movement of thesecond body (except for wild movements of the second body wherebycollisions occur, in which case there is a construction error).

In a preferred embodiment both the sensor and the actuator are mountedto a body that needs damping but not to each other (e.g., in the priorart both the sensor and the actuator are mounted in an assembly and thisassembly is mounted to the object to be damped). The disadvantage ofthis is that the performance becomes dependent on how well the assemblyis mounted to the body to be damped. Even in the best of cases this isalways limited. By giving the sensor and the actuator their owninterfaces, this dependency is removed. By mounting the sensor and theactuator parallel (instead of serially) with respect to each other, theobject to be damped is free of effects caused by deformations in thedamper (e.g., by a limited stiffness) since the sensor will only measuremovements of the object, without averse affects of deformations in thedamper due to actuator forces.

In another preferred embodiment both the sensor's line of action (or acombination of a multiple sensors) as well as that of the actuator arein the same point and the same direction (this is not the case in theprior art). This embodiment improves the damping of the body since adamping action is performed on the exact location where a disturbancehas been measured. The damping characteristics are improved even morewhen a disturbance can be predicted and an anticipated compensationsignal can be fed to a compensation means (e.g., electrical circuitryconnected to the actuator) of the damper.

Additional advantages and novel features will be set forth in thedescription which follows, and in part may become apparent to thoseskilled in the art upon examination of the following, or may be learnedby practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in further details, by way of examples, andwith reference to the accompanying drawings wherein:

FIG. 1 shows a system of a basic damper principle;

FIGS. 2A-B are diagrams showing an air mount performance of one on themarket;

FIGS. 3A-B are diagrams showing floor vibrations that are affecting amain plate;

FIG. 4 shows a diagram of a system that shows an improved air mount;

FIGS. 5A-C are diagrams of an open loop performance of a improved systemwith a controller;

FIGS. 6A-B are diagrams that illustrate a performance improvement animproved air mount system;

FIGS. 7A-B are diagrams that illustrate the sensitivity to floorvibrations;

FIG. 8 is a diagram that shows a traditional system's response to a 1[N] pulse;

FIG. 9 is a diagram that shows an improved system's response to a 1 [N]pulse;

FIG. 10 is a diagram that shows how long it takes to start an improvedsystem after a power down;

FIG. 11 is a presentation of a sum of potential and energy kineticenergy as an equivalent corresponding distance;

FIGS. 12A-C show an improvement of the system in a mid frequency rangeby using differentiating filter;

FIGS. 13A-B show a closed loop system response to forces on the mainplate of an improved system;

FIGS. 14A-B show responses of floor vibrations of an improved system;

FIG. 15 shows a time response for a pulse on the main plate of animproved system;

FIG. 16 shows a main plate's response of a pulse on the reference massof an improved system;

FIGS. 17A-B show a frequency repsonse function of the motion of the mainplante caused by forces on the reference mass of an improved system;

FIG. 18 shows a decay rate of the energy of the graph in FIG. 16;

FIG. 19 shows a damper of the invention with an actuator placedperpendicular to a sensor;

FIG. 20 shows a damper of the invention with an actuator placedperpendicular to a sensor whereby magnetical shielding has been applied;

FIG. 21 shows an absolute damper of the invention with a floating mass;and

FIG. 22 shows a schematic diagram of an active damper

DETAILED EMBODIMENTS

Limitations of the performance of an active isolation/cancellationsystem can be described using gain and phase relations from the controltheory.

FIG. 1 shows a diagram of a system 100 that illustrates a basic damperprinciple. Diagram 100 comprises a main plate 102 of about of 1000 [kg],a floor damper 104, a stiffness (also called floor spring) 106 and afloor 108. The main plate 102 and the floor 108 are connected with eachother via the stiffness 106 and damper 104. The stiffness 106 is o stiffthat it gives a resonance frequency of 1 [Hz]. The damper 104 value istypically such that it makes the whole system 100 critically damped. Theforce sensitivity of such a system is shown in FIG. 2.

At low frequencies a force of 1 [N] will give vibrations of less than 1[mm/s2]. Above 1 [Hz], the vibration amplitudes will be a constant 1[mm/s2]. This is reasonable air mount performance if one looks at whatis available in the market. Yet many companies complain that this is notgood enough. Disturbances are often more than 1 [N] and lithographicmachines and electron optical machines need a lower vibration level thanwhat is offered here.

A dominant error source of vibrations is the floor. The floor vibrationsare affecting the main plate via the floor damper and the floor spring.This effect is show in FIG. 3. A 10 micrometer floor vibration at 10[Hz] will give rise to a 10e−6[m]*500 [1/s2]=5[mm/s2] main platevibration.

FIG. 4 shows a diagram of a system 400 that includes an improved airmount. It involves the addition of a sensor 430 from the main plate 402to a reference mass 422, and an actuator 410 between the main plate 402and a floor 408. Other parts of the system comprise a floor damper 404,stiffness 406, another damper 424 and another stiffness 426. If thesensor 430 senses motion, then the actuator 410 is commanded such thatthe motion is reduced. This is, in effect, an extra damper. Referencemass 422 effectively functions as a means to indicate when themain-plate moves to the sensor and thereby inducing a signal in thesensor.

From previous electromechanical damper experience it is known that aperformance of 1e6 [Ns/m] can be made. In a typical but not exclusiveembodiment the reference mass is supported at 0.5 [Hz]. This electronicaddition needs a controller to allow us to make a stable system withhigh gains. A possible open loop performance of the new system withcontroller is given in FIG. 5. This is by not the only way to make itwork; it just serves as an example. Since the load is a 4th order system(actuator is attached to the first mass, sensor to the second), a totalof 360 degrees phase shift should be expected. A low frequencies thestiffness dominates, combined with a derivative action of the velocitysensor gives a +3 slope at low frequencies with +270 degrees phaseshift. Then two points of resonance can be seen, ending in a −1 slopewith a phase of −90 degrees. By adding a double local lag-lead filter atthe +slope, a stable system is obtained which will allow a substantialgain. Just to show off, in FIG. 5 a peak gain of 5e7 has been used. Inthe right hand side a polar plot is made of the open loop transferfunction. The Nyquist −1 point is encircled with a red circle withradius 0.5, which indicates the minimal stability margin. The greencircle has a radius of 0.5, which is a good distance for a damped timedomain response.

The performance improvement on the air mount system is substantial (seeFIG. 6). At low frequencies the start is the same. This is because herethe behavior is dominated by the stiffness of the floor spring, whichhas been kept identical. But the traditional damper started to improveat 1 [Hz], while the new damper does that at 0.003 [Hz]. At 1 [Hz], thevibration level is 1 [nm/s2] (improvement 1e6 times). The performanceremains significantly better up to and beyond 1000 [Hz]. At 1000 [Hz],the improvement is still a factor of 1000.

FIG. 7 shows a diagram that illustrates the sensitivity to floorvibrations. FIG. 7 shows that over a broad frequency range, theattenuation is a number of orders of magnitude better than thetraditional approach.

Due to the low frequent activities of the new approach, it will exhibita significant longer settling behavior than we find in the traditionalapproach. In FIG. 8 we find the traditional response to a 1 [N] pulse of0.1 [s] length given at 0.1 [s] after start of simulation. In FIG. 9 thesame for the new system.

The response of the active system has roughly a 1500 times loweramplitude, and a 300 times longer time scale. Both these numbers arebeneficial for the low acceleration level that we wanted, but there isreason for concern on how long it takes to start the system after apower down. A similar concern is how the system responds to adisturbance of the reference mass. To investigate this also a (huge) 1[N], 0.1 [s] pulse is administered to the reference mass in FIG. 10.Because the system is set up to follow the reference aggressively, asignificant main plate response results. In reality these huge forcesare never injected into the reference mass, but it is important tounderstand, that once the reference starts to move (for instance due tothe wake-up shock), it will continue to vibrate for a long time.

In FIG. 10, we see the slowly dying signal of the movements of thereference mass. We can try to find an expression that measures the speedof dying. This can be obtained through energy analysis. The residualvibrations can be modeled as a mass, damper and spring system. Then,given those parameters, we can compute the sum of potential energy (0.5k x²) and kinetic energy (0.5 m v²). This sum is presented as anequivalent corresponding distance ((0.5 x²+0.5 m v²/k)). This distanceis shown in FIG. 11. We see that at the end of 1200 seconds, there isstill a substantial distance to travel (0.1 [m]) before we are at rest.In addition, the rate of decline is slow.

Since the status of the reference mass must be assumed to be unknown atstartup, the above slow approach to tranquility is a disadvantage.Changes in the controller can improve this behavior. First of all, theresonance frequency of the reference mass is moved up to 10 [Hz]. Thiswill shift most of the suppression to the higher frequencies. As aresult there will be less performance at the lower frequencies, whichwill improve the low frequency recovery. In combination to the increaseof stiffness, the overall gain is also reduced. This aims to maintainthe high frequent suppression while lowering the low frequentsuppression. As a third measure, the distance of the open loop curve tothe −1 point is increased. This increase will introduce more damping inthe closed loop response. In order to improve the mid frequency range, adifferentiating filter is placed at 5 [Hz] and an integrating filter at50 [Hz]. See FIG. 12.

In FIG. 13 we find the closed loop system response to forces on the mainplate, FIG. 14 has the responses of floor vibrations.

The performance of the above systems is more modest, but still (in therange from 1 to 100 [Hz]) a factor of 10 better than the passive system.From 8 to 16 Hz, a 10 micron floor vibration will result in less than0.01 [mm/s2] main plate vibration. At 1 [Hz], the worst spot, it isstill a good 0.1 [mm/s2]. This is 5 times better than the passiveapproach. In FIG. 15 the time response is shown for a pulse on the mainplate. Compared with the passive system, the suppression is 15 timesbetter, and the settling time, 6 seconds, is 4 times longer, with 1.5more periods. Combined, this is a reduction of the acceleration of14*(4/1.5){circumflex over ( )}2=100 times!

in FIG. 16, the main plate's response of a pulse on the reference massis given. Also here the response time seems reasonable. The reason whythe behavior is better can in part be explained by FIG. 17.

FIG. 17 is the frequency response function of the motion of the mainplate caused by forces on the reference mass. We see a straight linefrom 0.2 [Hz] onwards, indicating that above this frequency, the mainplate is well slaved to the reference mass line (1/10 [kg] with a −180degrees phase shift from the force to displacement). Near 0.2 [Hz] wesee hardly any peaking, the system is well damped. Under 0.2 [Hz], thesystem shows a +3 slope. This means that the system is rapidlyinsensitive for frequencies that are lower than 0.2 [Hz]. Below 0.2[Hz], the reference mass communicates to the floor reference. This meansthat, depending on the amount of damping, we should expect to wait 5seconds or settling. With little damping this could easily become 50seconds, but in our system we have constructed sufficient damping tohave 90% of the energy gone after the first 5 seconds. After 5 seconds,we see no more vibration, but an exponential decay, indicating that oursystem is not a simple second order system, is a collection of differentparts, each with its own damped behavior.

We can also look at the decay rate of the energy of the graph in FIG.16. This is given by FIG. 18. We see that, from 9 [s] to 15 [s], theresidue distance reduces in a straight line from 2e-4 to 2e-5 [m]. Soevery 6 seconds the vibration level is reduced by a factor of 10. Thatis sufficiently quick for most power up sequences.

The air mount proposed is substantially better than the passive airmounts. The performance is a compromise between power up speeds anddamping performance. An implemented design, with a 10 [Hz] referencesupport and relative high frequent filters (near 0.5 [Hz], instead of0.002 [Hz]) and without any integrator seems to provide good results foran air mount. The invention enables an even better result. Certaincontrol options can be more optimized. There is also a possibility touse the last controller during start-up, and then once the system isstable and quiet, to switch over to a high performance controller. Thisis expected to provide better results.

The stiffness of the passive system between the main plate and the floordoes not play a significant role any more and can be relaxed. The dampercan be taken out completely. On the performance graphs we see nothingchange near the 2 [Hz] air mount resonance. Having the damper outreduces the transmission from floor vibrations into the main plate.Changing the stiffness will not affect the force sensitivity, but itwill affect the floor transmissibility.

The mass of the reference is not important, but the resonance frequencyis because it determines where most of the improvement will be.

The lower the mechanical damping of the reference, the more mobile it isand the more sensor signal is generated. This is why, in FIGS. 6 and 7,there is a dip at 0.5 [Hz].

The application specific tuning that is foreseen is the tuning of themass and stiffness of the payload (rigid body mode) and the tuning ofthe feed forward signals. Removing the cross talk between the dampers isan identical procedure as tuning the feed forward.

FIG. 19 shows a diagram of a damper comprising an actuator coil 1910placed perpendicular to a pair of sensor coils 1920. The actuator 1910and the sensors 1920 are connected an object to be damped 1930. Byplacing the actuator 1910 and the sensors 1920 perpendicular to eachother, unwanted cross talk is minimized (e.g., EM cross talk in case thesensor and the actuator are both of a Lorenz type of coil) since thevectors of the EM-fields of the sensor and actuator coils are 90 degreesfrom each and therefore they can not see each other's EM-field.

FIG. 20 shows a diagram similar to that of FIG. 19 but now an additionalmagnetical cross talk countermeasure has been applied. FIG. 20 comprisesof a damper comprising an actuator 2010 placed perpendicular to a pairof sensors 2020, an object to be damped 2030 and a magnetical shielding2040. The magnetical shielding comprises a material of μ-metal and istypically placed around the sensor coils that are part of sensors 2020.This magnetical shield can also have a conductive layer to minimize theEM crosstalk from the actuator or from the environment. This shield canalso be given mass and stiffness to attenuate any acoustical disturbancefrom the environment.

FIG. 21 shows an absolute damper of the invention with a floatingreference mass. FIG. 21 comprises an actuator-coil 2110, anactuator-magnet 2150 mounted on arms 2160 that are connected to floor2170, an object to be damped 2130 on which sensor-coil 2120 is mountedand on which magnet assembly 2180 that is connected by springs 2190.Magnet assembly 2180 comprises a reference mass and a sensor-magnet.Magnet assembly 2180 may also comprise a magnetical as well as anelectrical shielding that shield the sensor (comprising coil 2120 andthe sensor-magnet) from the actuator (comprising actuator coil 2110 andthe actuator-magnet 2150) and from other external electrical ormagnetical disturbances.

FIG. 22 shows a schematic diagram of an active damper. FIG. 22 comprisesa sensor coil 2220, an actuator-coil 2210, a sensor magnet 2280, anactuator-magnet 2250, and an object to be damped 2230. Magnets 2250 aremounted to the floor 2270. Magnets 2280 are mounted to a reference mass.Coils 2250 and 2220 are mounted in a stiff manner to an object to bedamped 2230. Sensor coil 2210 produces an electrical signal I-s uponmovement relative to sensor magnet 2280. In this example of the activedamper, an electrical controller comprises a low-pass filter amplifierand a high-pass filter amplifier to which signal I-s is fed. Many othertypes of electrical controllers exist and can be applied for theinvention. The outputs of the amplifiers are added and result inelectrical signal I-a. Amplification and filter parameters can beadjusted and dimensioned according to parameters of a system of whichthe active damper is a part. Electrical signal I-a will induce amovement of actuator coil 2210 relative to actuator magnet 2250. Theactive damper is only then properly adjusted and dimensioned when it canisolate a vibration and cancel the vibration in a desired frequencyrange with a desired damping characteristic. Although the damper shownin FIG. 22 is of a relative type most of the electrical controller canbe used for an absolute damper as well.

What is claimed is:
 1. A damper system, comprising: a sensor that canmeasure a mechanical vibration and is capable of producing an electricalsignal caused by the vibration and wherein the sensor is designed to bemounted between a body and a reference mass; an actuator responsive tothe electrical signal thereby producing a force between the body and anexternal body; wherein the sensor and the actuator are locatedsubstantially close to each other thereby having a substantially smalldelay; wherein the delay substantially consists of the sum of anacoustic signal delay and an electronic signal delay in the actuator andthe sensor.
 2. The system of claim 1, wherein the sensor comprises aLorenz type coil with magnet pair and the actuator comprises a Lorenztype of coil with magnet pair.
 3. The system of claim 1, wherein a lineof action of the sensor coincides with a line of action of the actuator.4. The system of claim 1, further comprising: an acoustical shieldingplaced such that acoustical airwaves are substantially attenuated beforereaching the reference mass of the sensor.
 5. The system of claim 2,wherein the coils are placed such that their induced magnetic fields aresubstantially perpendicular.
 6. The system of claim 2, wherein multiplesensor coils are positioned such that a magnetical field disturbanceoriginating from at least one of the actuator coil and an externalsource is substantially cancelled by one of subtraction and addition ofthe sensor signal.
 7. The system of claim 2, further comprising: amagnetical shielding placed such that an EM field induced by theactuator is substantially attenuated.
 8. The system of claim 2, furthercomprising: a electrical shielding placed such that an EM field inducedby the actuator is substantially attenuated.
 9. The system of claim 1,wherein the delay is less than about 1 millisecond.
 10. The system ofclaim 1, wherein the delay is less than about 500 microseconds.
 11. Thesystem of claim 1, wherein the delay is less than about 50 microseconds.12. An apparatus, comprising: an active vibration isolation andcancellation absolute damper mounted between a body to be damped and oneof a floor and another body that acts as receiver for the reactionforces, comprising: a sensor that can measure a mechanical vibration andis capable of producing an electrical signal caused by the vibration andwherein the sensor is designed to be mounted between the apparatus andan external mass; and an actuator responsive to the electrical signalthereby producing a force between the body and one of the floor and theother body that acts as a receiver for reaction forces; wherein thesensor and the actuator are located substantially close to each otherthereby having a substantially small acoustic delay between the actuatorand the sensor; wherein the delay substantially consists of the sum ofan acoustic signal delay and an electronic signal delay in the actuatorand the sensor.
 13. The apparatus of claim 12, wherein the sensorcomprises a Lorenz type coil and the actuator comprises a Lorenz type ofcoil.
 14. The apparatus of claim 12, wherein a line of action of thesensor coincides with a line of action of the actuator.
 15. Theapparatus of claim 12, further comprising: an acoustical shieldingplaced such that an acoustical airwave is substantially attenuatedbefore reaching the sensor.
 16. The apparatus of claim 13, whereby thecoils are placed such that their induced magnetic fields aresubstantially perpendicular.
 17. The apparatus of claim 13, furthercomprising: a magnetical shielding placed such that an EM field inducedby the actuator is substantially attenuated.
 18. The apparatus of claim13, further comprising: a electrical shielding placed such that an EMfield induced by the actuator is substantially attenuated.
 19. Theapparatus of claim 12, wherein the delay is less than about 1millisecond.
 20. The apparatus of claim 12, wherein the delay is lessthan about 500 microseconds.
 21. The apparatus of claim 12, wherein thedelay is less than about 50 microseconds.
 22. A method of activelydamping a body from vibration, the method comprising: measuring amechanical vibration with a sensor; producing an electrical signalcaused by the vibration and wherein the sensor or is designed to bemounted between the body and a reference mass; using an actuator forresponding to the electrical signal thereby producing a force betweenthe body and an external body; and using the sensor and the actuator,placed substantially close to each other thereby having a substantiallysmall delay; wherein the delay substantially consists of the sum of anacoustic signal delay and an electronic signal delay in the actuator andthe sensor.
 23. The method of claim 22, wherein the delay is less thanabout 1 millisecond.
 24. The method of claim 22, wherein the delay isless than about 500 microseconds.
 25. The method of claim 22, whereinthe delay is less than about 50 microseconds.
 26. The method of claim22, wherein the sensor comprises a Lorenz type coil with magnet pair andthe actuator comprises a Lorenz type of coil with magnet pair.
 27. Themethod of claim 22, wherein a line of action of the sensor coincideswith a line of action of the actuator.
 28. The method of claim 26,wherein the coils are placed such that their induced magnetic fields aresubstantially perpendicular.
 29. The method of claim 26, whereinmultiple sensor coils are positioned such that a magnetical fielddisturbance originating from at least one of the actuator coil and anexternal source is substantially cancelled by one of subtraction andaddition of the sensor signal.
 30. A system for control of a movement ofa body relative to a reference, wherein the system comprises: a sensorfor supplying a sensor signal representative of the movement; anactuator for affecting the movement under control of the sensor signal;sensor and the actuator are arranged so close to one another that adelay time characterizing the control of the movement is smaller than 1millisecond and depends substantially only on an acoustic couplingbetween the sensor and the actuator.
 31. The system of claim 30, whereinthe delay time is less than 500 microseconds.
 32. The system of claim30, wherein the delay time is less than 50 microseconds.
 33. The systemof claim 30, for use in a manufacturing of integrated circuitry.
 34. Thesystem of claim 30, for damping the movement.
 35. The system of claim30, wherein the sensor comprises a Lorenz type coil with magnet pair andthe actuator comprises a Lorenz type of coil with magnet pair.
 36. Thesystem of claim 35, wherein the coils are placed such that their inducedmagnetic fields are substantial perpendicular.
 37. The system of claim35, wherein multiple sensor coils are positioned such that a magneticalfield disturbance originating from at least one of the actuator coil andan external source is substantially cancelled by one of subtraction andaddition of the sensor signal.
 38. The system of claim 30, wherein aline of action of the sensor coincides with a line of action of theactuator.